 <!-- class 加上 show_flex 显示 -->
<nav >
    <div class="left_area">
        <div class="back_button" ng-click='backEvent()' ng-class="{showBacckBtn: isShowBtn , noImg: isNoImg}" ng-bind="tipBackMsg">返回</div>
    </div>
    <div class="middle_area">
        <div class="title" ng-bind="titleName"></div>
    </div>
    <div class="right_area">
        <div class="more" ng-if="isMore"></div> 
    </div>
</nav>